This application claims the benefit under 35 U.S.C. § 119 of Korean Patent Application No. 10-2004-0024503, filed on Apr. 9, 2004, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor and an electrophotographic imaging apparatus employing the photoreceptor. More particularly, the invention is directed to an electrophotographic photoreceptor containing a naphthalenetetracarboxylic acid diimide derivative having high solubility in organic solvents and strong compatibility with polymer binder resins to provide strong electron transporting ability. The invention is further directed to an electrophotographic imaging apparatus employing the naphthalenetetracarboxylic acid diimide derivative.
2. Description of the Related Art
In electrophotography that is used in laser printers, photocopiers, CRT printers, LED printers, liquid crystal printers etc., an electrophotographic photoreceptor in the form of a plate, disk, sheet, belt, drum or the like includes an photosensitive layer formed on an electrically conductive substrate. In electrophotography, the electrophotographic photoreceptor is imaged by first uniformly electrostatically charging the surface of the photosensitive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas where light strikes the surface, thereby forming a pattern of charged and uncharged areas, referred to as a latent image. A liquid or solid toner is then provided in the vicinity of the latent image, and toner droplets or particles deposit in the vicinity of either the charged or uncharged areas to create a toned image on the surface of the photosensitive layer. The resulting toned image can be transferred and fixed to a suitable ultimate or intermediate receiving surface, such as paper, thereby completing the formation of an image. The residual toner is then cleaned and residual charges are erased from the electrophotographic photoreceptor. Thus, the electrophotographic photoreceptor can be repeatedly used for long periods of time.
The electrophotographic photoreceptor includes an inorganic photoreceptor in which an inorganic material such as selenium or amorphous silicon is used in a photosensitive layer, and an organic photoreceptor in which an organic material is used in a photosensitive layer. The organic photoreceptor can be easily manufactured. A charge generating material (CGM), a charge transporting material (CTM), and a binder resin can be selected from a wide variety of respective candidate materials to provide a high degree of freedom in designing the photoreceptor.
Electrophotographic photoreceptors are widely categorized into two types. The first is a laminated-type having a laminated structure including a charge generating layer comprising a binder resin and a CGM, and a charge transporting layer comprising a binder resin and a CTM (mainly a hole transporting material (HTM)). In general, the laminated-type electrophotographic photoreceptor is used in the fabrication of a negative (−) type electrophotographic photoreceptor in which the charge generating layer and the charge transporting layer are sequentially laminated on the electrically conductive substrate. The second type is a single layer type in which a binder resin, a CGM, a HTM and an electron transporting material (ETM) are dispersed in an electophotosensitive layer. In general, the single layer-type organic photoreceptor is used in the fabrication of a positive (+) type electrophotographic photoreceptor.
The (+) type single layered electrophotographic photoreceptor has the advantage in that it generates a small amount of ozone that is harmful to humans. In addition, the (+) type single layered photoreceptor has a single photosensitive layer so that the production costs are low. The most essential material among the materials in the (+) type single layered electrophotographic photoreceptor is the ETM. Since the hole transporting ability of the HTM is 100 times greater than the electron transporting ability of the commonly used ETM, the performance of the single layered electrophotographic photoreceptor is dependent upon the electron transporting ability of the ETM.
The electron transporting ability of the ETM is considerably influenced by the solubility in organic solvents and the compatibility with polymer binder resins of the photosensitive layer. Widely known conventional ETMs include dicyanofluorenone derivatives having the formula (i) below and naphthalenetetracarboxylic acid diimide derivatives having the formula (ii) below.
                in which R3′ is a substituted or unsubstituted alkyl or aryl group.        
                in which R1′ and R2′ are independently a substituted or unsubstituted alkyl group, or a substituted or unsubstituted cyclic alkyl group.        
However, dicyanofluorenone derivatives have low solubility in organic solvents and poor electron transporting ability. Thus, when fabricating an electrophotographic photoreceptor using these materials as the ETM, the electrophotographic photoreceptor has disadvantages such as a reduced charging potential and an increased exposure potential after long periods of repeated use. Meanwhile, it is known that the naphthalenetetracarboxylic acid diimide derivatives disclosed in U.S. Pat. Nos. 4,992,349 and 5,468,583 exhibit an electron transporting ability better than naphthoquinone derivatives, which have been conventionally used as the ETM. U.S. Pat. Nos. 4,992,349 and 5,468,583 are hereby incorporated by reference in their entirety. However, the naphthalenetetracarboxylic acid diimide derivatives have low solubility in organic solvents and poor compatibility with polymer binder resins, and thus still have a poor electron transporting ability. Thus, when fabricating an electrophotographic photoreceptor, in particular, a single layered electrophotographic photoreceptor, using these materials as the ETM, the electrophotographic photoreceptor has problems such as a reduced charging potential and an increased exposure potential after long periods of repeated use.